Study On A Novel Dynamic Vibration Absorber Based On The First Kind Of Levitation Characteristics Of Ferrofluid

As China’s manned space program is entering the stage of space station construction,some vibration problems of flexible overhanging structures,such as solar panels,antennae,flexible robotic arms,and heat radiators,will become increasingly prominent.Meanwhile,the ferrofluid dynamic vibration absorber is very suitable for solving these vibration problems,owing to the advantages of its simple and reliable structure,long service life,high sensitivity to inertia force,zero electrical energy consumption,and no fatigue which exists in metal elastic elements.In order to overcome the failure problem resulting from the interference of the external magnetic field or magnetic material in the traditional ferrofluid dynamic absorber,according to the first kind of levitation characteristics of ferrofluid,this dissertation proposes a novel ferrofluid dynamic vibration absorber,and investigates its performances in three aspects including theory,simulation and experiment.The main work is shown as follows:(1)The dynamic model of the ferrofluid dynamic vibration absorber is built.Based on this damping coefficient of the main system,three basic elements including the inertial mass block with a value of 0.208kg,the elastic element with an optimal stiffness coefficient value of 9.41N/m and the damping element with an optimal damping coefficient value of 0.517kg/s are determined by a set of optimization equations.(2)The key components and the overall structure of the ferrofluid dynamic vibration absorber are designed,and the mathematical relationships between dimensions of different parts of the device are obtained.During the design process,the necessary conditions for the stable levitation of the inertial mass block are given,and the spatial magnetic field distribution resulting from the magnet installed in a magnetic shell is derived.Furthermore,the dimension parameters of the magnet and the magnetic shell are optimized with the heip of the software COMSOL.Finally,the correctness of simulation result is verified by the experiment.(3)A mechanical model,taking into consideration the mass of the ferrofluid,the intensity of the magnetic field,the geometric parameters of the inertial mass block and the shell,is established to analyze the axial and radial buoyant forces acting on the inertial mass block in a relevant environment(ground or space).According to the mechanical model,the force balance and the moment balance of the inertial mass block in both ground and space environment are analyzed.Then the factors which affect the stability of the levitation of the inertial mass block are obtained.In addition,the levitation state and the levitation process of the inertial mass block in the ground environment are investigated.(4)A tester is constructed to measure the axial and radial buoyant forces acting on the inertial mass block in the ferrofluid dynamic vibration absorber with different structural parameters,and the structural parameters which make the radial buoyant force meet the optimal stiffness in a relevant environment(ground or space)is obtained.The linearity of the radial buoyant force is also investigated,with the minimum value is 17.84%in the ground environment and 4.49%in the space environment,respectively.(5)The distribution of magnetic field and ferrofluid in the ferrofluid dynamic vibration absorber is simulated with the help of the software COMSOL.It is found that the surface boundary configuration of the ferrofluid is in good agreement with the iso-magnetic-field line.The result illustrates that the influence of the gravity and the surface tension on the surface boundary configuration of the ferrofluid can be neglected.(6)The magnetoviscous effect of the ferrofluid is investigated and measured,when the magnetic field and the vorticity are perpendicular.Through deriving the flow field of the ferrofluid,the viscous shear force acting on the inertial mass block is obtained.The transfer Sunction of the inertial mass under step force is deduced,based on which an apparatus is constructed,where the damping coefficient of the ferrofluid dynamic vibration absorber under different environments and parameters is measured.The experimental results show that the damping coefficient with a value of 0.54kg/s is closest to the optimal value.(7)The vibration characteristics of the ferrofluid dynamic vibration absorber under different initial amplitudes are studied by means of the free vibration of a copper plate.The results show that:In the ground environment,for the used ferrofluid dynamic vibration absorbers,the theoretical results are in good agreement with the experimental results,and the measurement results of the time percentage of vibration attenuation are above 94.7%,with the maximum value of 97.73%.On the other hand,in the space environment,for the utilized ferrofluid dynamic vibration absorbers,the theoretical results of the time percentage of vibration attenuation are above 98.75%,with the maximum value of 99.46%.